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Article

Construction of Multi-Defective ZnMn2O4/Carbon Nitride Three-Dimensional System for Highly Efficient Photocatalytic Sulfamethoxazole Degradation

by
Yandong Xu
1,
Jianjun Liao
1,*,
Linlin Zhang
1,*,
Yakun Li
2 and
Chengjun Ge
1
1
Key Laboratory of Agro-Forestry Environmental Processes and Ecological Regulation of Hainan Province, School of Ecology and Environment, Hainan University, Haikou 570228, China
2
Shandong Ocean Chemical Industry Scientific Research Institute, Weifang 262737, China
*
Authors to whom correspondence should be addressed.
Catalysts 2023, 13(1), 172; https://doi.org/10.3390/catal13010172
Submission received: 11 November 2022 / Revised: 8 January 2023 / Accepted: 9 January 2023 / Published: 11 January 2023
(This article belongs to the Special Issue Advanced Catalysis for Green Fuel Synthesis and Energy Conversion)
Browse Figures
Review Reports Versions Notes

Abstract

:
Rational design of composite nanostructured photocatalytic systems with good sunlight absorption capacity and efficient charge separation and transfer ability is an urgent problem to be solved in photocatalysis research. Here, a ZnMn2O4 decorated three-dimensional carbon nitride with O, C co-doping, and nitrogen defect composite photocatalytic system was prepared using a simple hydrothermal method and subsequent calcination method. For the photocatalytic reactions, the presence of heterostructures, C, O co-doping, and nitrogen defects greatly promotes the separation and transfer of charges at the semiconductor/semiconductor interface under the local electric field, thereby extending its service life. The photocatalytic degradation efficiency of sulfamethoxazole in water is as high as 94.3% under the synergistic effects, which is also suitable for the complex water environment. In addition, the synthesized photocatalyst has good chemical stability and recyclability. This study provides a new opportunity to solve the problem of environmental pollution.

1. Introduction

In recent years, environmental pollution has been regarded as an important challenge facing humankind with the development of society and the continuous improvement of human living standards [1]. Sulfamethoxazole (SMX), as a common antibiotic [2], is widely used in human medicine [3]; however, it has extremely poor adsorption and degradation capacity in human and animal intestines. It is undeniable that the antibiotics can still exist stably in the environment, easily cause ecotoxic effects [4], seriously damage the safety of ecosystems [5], and threaten human health [6]. The treatment of sulfonamide antibiotics is inevitable, but traditional biological wastewater treatment methods cannot implement the resistance caused by the antibacterial properties of SMX [7].
Semiconductor photocatalysis technology, as an ideal technology, can rely on solar energy to generate a series of redox-active substances (photogenerated electrons, photogenerated holes, hydroxyl radicals, and superoxide radicals, etc.) to achieve the purpose of sulfonamides antibiotics degradation and ecological restoration [8,9]. Among many photocatalysts, carbon nitride is frequently applied in photocatalytic fields, such as photocatalytic hydrogen evolution [10] and photocatalytic carbon dioxide reduction [11], etc., especially in the direction of photocatalytic degradation of organic pollutants [12] because of its good band gap structure, excellent chemical stability, and environmental friendliness [13,14,15,16]. Although great progress has been made in its preparation, the catalytic efficiency of g-C3N4 is still poor due to the fast recombination of photogenerated carriers and insufficient absorption range of light [17]. Various strategies have been proposed to improve the photocatalytic activity of carbon nitride. The introduction of defect engineering has a great influence on the electronic structure and is an effective strategy to optimize the oxygen activation active center and regulate the interfacial charge transfer [18,19,20]. Wu et al. enhanced light absorption and promoted charge separation by introducing N vacancies on C3N4, resulting in a H2O2 production rate of 10.2 mmol/h/g, 89.5 times that of the original C3N4 [21]. The multi-vacancy carbon nitride developed by Liang et al. can efficiently and selectively photocatalyze the C–C bond in lignin, and the carbon vacancy can be used as a trapping site to inhibit photogenerated charge recombination, resulting in C3N4 having a higher N content and therefore more readily oxidizing Cβ-H [22].
In addition to defect engineering, the formation of heterojunction can also improve the charge transfer efficiency, which is beneficial for producing more active free radicals [23,24]. Shen et al. designed the CF/C3N4/Bi2MoO6 using a thermal condensation-solvothermal method, which gave the maximum redox potential at the interface heterojunction and could efficiently degrade 86% of antibiotics in a short time [25]. In order to pursue higher catalytic activity, carbon nitride needs to combine semiconductors with a more negative CB potential. Zinc manganate is an attractive material. As a new type of semiconductor material, it not only has the advantages of suitable band gap, environmental friendliness, and low cost, but can also provide higher energy density [26,27]. The defect engineering and heterojunction formation can effectively improve the photocatalytic activity of carbon nitride. However, most of the reported samples were developed in a complex process. In this regard, it is necessary to develop a simple method to precisely tune the structure of carbon nitride.
In this work, we prepared nitrogen-deficient, oxygen and carbon co-doped three-dimensional ZnMn2O4/carbon nitride (ZMOCNs) composites using a simple hydrothermal method and subsequent calcination method, and then systematically studied the effect of ZnMn2O4 doping on photocatalytic degradation of SMX. The composite of ZnMn2O4 improved the adsorption and carrier transfer/separation ability of O2, thus greatly improving the degradation efficiency of SMX. This multi-defect synergistic heterojunction strategy provides potential for future treatment of persistent organic compounds.

2. Results

2.1. Structural Characterization and Analysis

As shown in Figure 1a, Figures S1 and S2, the crystal structure of ZMOCNs composites were analyzed using XRD. The pure ZnMn2O4 has strong diffraction peaks at 29.3, 31.3, 33.0, 36.9, 38.9, 44.8, 59.1, 60.9, and 64.8°, corresponding to the (1 0 1), (1 1 2), (2 0 0), (1 0 3), (2 1 1), (2 2 0), (3 0 3), (3 2 1), and (2 2 4) planes of monoclinic ZnMn2O4 (JCPDS 24-1133) [28]. Two strong and sharp characteristic peaks appear at 13.01° and 27.22°, which correspond to the (1 0 0) and (0 0 2) crystal planes of multi-defect C3N4 (JCPDS No. 87-1526) [29], respectively. In addition, the angle of the XRD peak of the C3N4 with multiple defects is slightly shifted, which may be due to the larger cell parameters for adapting to the larger O heteroatom embedding. The broadening and weakening of the (0 0 2) peak may be due to the substitution of N atoms with the C and O atoms [30]. For the ZMOCNs composites, the XRD patterns contain both the diffraction peaks of C3N4 and ZnMn2O4, and the peak intensity of C3N4 gradually decreases with the increase of zinc manganate content, which may be caused by the sharp characteristic peak of pure ZnMn2O4. In addition, a slight shift of the characteristic peak of ZnMn2O4 in the composite was observed compared with that of pure zinc manganate, indicating that a heterojunction was formed between zinc manganate and carbon nitride, and electron transfer existed. XRD results showed that the composite photocatalyst was successfully constructed.
The contents of Zn and Mn in ZMOCNs were studied using ICP. The result was shown in the Table S1. According to the ICP test results, the prepared ZMOCNs particles meet the designed mass ratio.
In addition, to further verify the structure of composite materials, FT-IR was used to test the materials. The FT-IR characteristic peaks of C3N4, ZnMn2O4 and ZMOCNs are shown in Figure 1b. In the C3N4 and ZMOCNs, a large absorption peak at 3000~3500 cm−1 can be found, which is caused by the O-H stretching vibration and N-H stretching vibration of the water molecules adsorbed on the material. The absorption peak in the range of 1649~1245 cm−1 is attributed to the tensile vibration absorption peak which may be caused by the triazine structure repeating unit in C3N4 and ZMOCNs and the N-(C)3 or C-NH-C structure. The peak at 800 cm−1 is caused by the in-plane stretching vibration of the triazene part. The ZnMn2O4 and ZMOCNs show a characteristic peak at 505 cm−1, which is mainly caused by the stretching vibration of Mn-O. The above results proved the successful synthesis of ZnMn2O4, C3N4 and the composite materials.
In addition, to further verify the successful preparation of the material, 50 wt% ZMOCN material was used as an example for XPS analysis. Figure 2a shows the survey XPS spectra of the ZMOCN material, and it is detected that the material has five characteristic peaks of C, N, O, Zn and Mn. The C 1s spectra of the ZMOCN shows three main peaks at 284.8, 286.2, and 289.2 eV (Figure 2b). The main peak at 284.8 eV can be attributed to an exogenous carbon and C–H bond. The peaks at 286.2 and 289.2 eV are attributed to the C-N-C and N-C=N backbones in C3N4, respectively [31]. In Figure 2c, the three characteristic peaks of the material can be clearly observed in the N 1s spectrum of the material which are located at 398.9, 400.5, and 401.7 eV, corresponding to the C=N-C, N-(C)3 and C-N-H functional groups of the material, respectively. For the O 1s spectrum, as shown in Figure 2d, four fitted peaks appear at 529.8, 530.0, 531.3, and 532.9 eV, corresponding to the representative metal–oxygen bond, hydroxyl bond, lattice oxygen, and C–O bond, respectively [32]. C–O bond confirms the introduction of oxygen atoms in the material. Figure 2e represents the Zn 2p spectrum of the material. It can be seen that two peaks at 1024 and 1047 eV can be attributed to Zn 2p3/2 and Zn 2p1/2 of Zn, respectively [33]. Five characteristic peaks were observed in Figure 2f, which were 642.1, 653.7, 640.9, 652.9, and 654.1 eV, corresponding to Mn 2p3/2, Mn 2p1/2, Mn2+, Mn3+ and Mn4+, respectively [34]. The XPS, XRD and FT-IR results are consistent, which further proves the successful synthesis of C and O co-doped and nitrogen-deficient ZMOCNs composites.
EPR spectra of the pure C3N4 and ZMOCN-50wt% was determined to prove the existence of N defect. As shown in Figure 3a, it is obvious that the pure C3N4 and ZMOCN-50 wt% produce symmetrical EPR signals at g = 2.004, indicating that both materials have nitrogen defects. Based on the above results, the successful preparation of ZMOCNs composites with nitrogen defects was proved. In Figure S3, the optical absorption edge of pure C3N4 nanosheets is about 459 nm, while the optical absorption edge of multi-deficient C3N4 is red-shifted to 593 nm, which may be caused by C, O co-doped, and nitrogen defects. According to the calculation, the band gap energy of C3N4 with multi-deficient and pure C3N4 is 1.43 and 2.84 eV, respectively (Figure S4).
The UV-Vis spectra of ZMOCNs composites are shown in Figure 3b. As the content of zinc manganate nanomaterials increases gradually, the absorption range of ZMOCNs composites shows a red shift first and then a blue shift. Among them, the utilization rate of visible light of 50 wt% ZMOCN composites is the largest. The reason for this phenomenon may be due to the structural stability of the 50 wt% ZMOCN composite material and the uniform loading of zinc manganate, which accelerates the separation of electrons and holes in the composite material and improves the electron transfer rate, thereby improving the utilization of visible light by the material. In addition, the calculated band gap energies of 10 wt% ZMOCN, 30 wt% ZMOCN, 50 wt% ZMOCN, 70 wt% ZMOCN, and 90 wt% ZMOCN are 1.59, 1.43, 1.24, 1.33, and 2.02 eV, respectively (Figure 3c). It reflects that the 50 wt% ZMOCN composite material can effectively inhibit the recombination of photogenerated electron-hole pairs, thereby improving the photocatalytic performance of the material, improving the degradation ability of the material, and achieving an environmentally friendly effect.
The flat band potentials of C3N4 and ZnMn2O4 were calculated using the Mott–Schottky equation (Figure S5). The positive slope of Figure S4a indicates the n-type property of C3N4, and the negative slope of Figure S4b indicates the p-type property of ZnMn2O4. In addition, the EF values of C3N4 and ZnMn2O4 were determined to be −0.41 and 0.23 eV (vs. Ag/AgCl), respectively. According to the formula: ENHE = EAg/AgCl + E0Ag/AgCl, where E0Ag/AgCl = 0.2 eV, the EF values of C3N4 and ZnMn2O4 are calculated as −0.21 and 0.43 eV (vs. NHE), respectively. Typically, the EF of an n-type semiconductor is close to its CB, whereas the EF of a p-type semiconductor is roughly equivalent to its VB. Therefore, the VB of C3N4 and CB of ZnMn2O4 are 1.22 and −1.5 eV (vs. NHE), respectively.

2.2. Morphology Analysis

Figure S6 shows the SEM images and Figure S7a shows the TEM images of C, O doped C3N4 with nitrogen defects. Obviously, the C3N4 synthesized with cotton as a template presents a three-dimensional network structure, the surface particles are rough and uniform, and there is no obvious agglomeration. The Figure S7b–d is the mapping diagram of C, O doped C3N4 with nitrogen defects. The three elements of C, N, and O are evenly distributed, which is consistent with the previous XRD and XPS results, proving that the synthesis route produces a three-dimensional porous C, O-doped nitrogen-deficient C3N4 material. The SEM images and the TEM images of ZnMn2O4 were provided in Figures S8 and S9. The ZnMn2O4 is a nanosheet structure with a size of 50–100 nm. The SEM images of ZMOCNs (Figure 4a–e) show that the surfaces of 10 wt% ZMOCN, 30 wt% ZMOCN, and 70 wt% ZMOCN surfaces are not uniformly adhered with some areas of agglomeration. When the mass fraction is 90 wt%, the three-dimensional structure of the material is covered. In particular, the three-dimensional structure of the material is obvious, the particle load is uniform, and no obvious aggregation occurs when the mass fraction is 50 wt%. Figure 4f display the TEM image of 50 wt% ZMOCN. It can be clearly seen that 50 wt% ZMOCN has obvious pores and a clear three-dimensional structure without agglomeration. In summary, the three-dimensional structure of the material is optimal when the mass fraction of zinc manganate in the composite is 50 wt%.

2.3. Photocatalytic Activity and Mechanism

The photocatalytic activity of the samples was evaluated using the degradation of SMX under visible light (λ ≥ 420 nm) irradiation. The photocatalytic degradation process of SMX was monitored using the change of the UV-visible absorption spectrum of SMX solution. The intensity of the characteristic absorption peak (260 nm) decreased with time. As shown in Figure 5a, the degradation efficiency of ZMOCNs composites was significantly higher than those of the C3N4 and ZnMn2O4. With the increase of ZnMn2O4 mass fraction, the photocatalytic degradation activity of ZMOCNs increased. When the mass fraction of ZnMn2O4 is 50 wt%, the photocatalytic degradation efficiency is the highest, which is about 94.3%. However, the photocatalytic degradation efficiency gradually decreases when the mass fraction of ZnMn2O4 exceeds 50 wt%. This indicates that the addition of a certain amount of ZnMn2O4 can form a heterojunction with efficient carrier transport, thereby improving the overall photocatalytic activity. When ZnMn2O4 is added excessively, the three-dimensional structure of the material is covered and a large number of agglomerations occur, reducing the carrier transport capacity and the photocatalytic activity of the material.
Figure 5b shows that the ZMOCN-50 wt% composite exhibits a high photocatalytic activity for SMX in most water environments such as deionized water, tap water, river water, and seawater. To investigate the stability of SMX degradation by the prepared composite photocatalyst ZMOCN-50 wt%, multiple cycles of SMX degradation experiments were carried out. As shown in Figure 5c, ZMOCN-50 wt% can still degrade 84.7% of SMX after the 4th cycles (4 h). To study free radicals involved in photocatalytic reactions, the photogenerated holes, superoxide radicals, and hydroxyl radicals were quenched with EDTA-2Na, p-benzoquinone and t-Butanol, respectively (Figure 5d). In the presence of EDTA-2Na, the degradation efficiency of SMX by ZMOCN-50 wt% decreased from 94.3% to 15.6%. After adding p-benzoquinone to the experiment, the degradation efficiency of SMX by ZMOCN-50 wt% also decreased to 24.1%. In contrast, the presence of t-Butanol had little effect on the degradation of SMX by ZMOCN-50 wt%, and the degradation rate reached 85.5% after 60 min. It can be seen that the free radicals that play a major role in the photocatalytic reaction are holes and superoxide radicals.
In addition, the generation of reactive oxygen species on ZMOCN-50 wt% under visible light irradiation was monitored using EPR. As shown in Figure 6a,b, the EPR signal cannot be detected in the dark, but after 6 min of visible light irradiation, two four-wire EPR signals with intensity ratios of 1:1:1:1 and 1:2:2:1 were clearly observed. In summary, ZMOCN-50 wt% degradation of SMX mainly relies on the photogenerated holes and superoxide radicals, in which hydroxyl radicals participate in the degradation reaction but are not the main degradation substances. This is the same as the results of free radical capture experiments.
According to the results of LC-MS (Figure S10), three intermediates (m/z 100~300) were identified. The proposed degradation pathway is shown in Figure 7. Overall, SMX degradation tends to break three different chemical bonds. First, the amino group of SMX is oxidized directly during the reaction to form P1. The amino benzene ring of SMX is then further oxidized to form P2. In addition, the S–N bond (sulfonamide bond) may have been broken, resulting in oxidation of the aminobenzene ring product (P3). These intermediates are gradually broken down into small organic molecules and eventually mineralized into small inorganic molecules.
The ECOSAR program is used to predict the acute and chronic toxicity of SMX and its intermediates. The toxicity of compounds can be classified according to the Globally Harmonized System of Classification and Labeling of Chemicals. As shown in Figure 8, SMX shows different toxicity levels to different species. In terms of acute toxicity, the initial intermediate P3 of the degradation pathway is harmful to water fleas and algae, while all intermediates are basically harmless to fish. For chronic toxicity, intermediate P1 is harmful to fish and daphnia, but still toxic to algae. In addition, the LC50, EC50, and ChV values of most intermediates were higher, indicating that the toxicity of SMX was significantly reduced after degradation, and the intermediate P2 was even harmless. In summary, the ecotoxicity of SMX was significantly reduced after degradation in the ZMOCNs system.

3. Discussion

Based on the above experimental results, a possible z-type heterojunction mechanism is proposed (Figure 9). According to the experimental results, the CB and VB positions of C3N4 and ZnMn2O4 can be determined (ECB is −0.21 and −1.5 eV vs. NHE, EVB is 1.22 and 0.43 eV vs. NHE, respectively). Therefore, C3N4 and ZnMn2O4 easily form an Z-type heterojunction. Under visible light irradiation, the valence band (VB) electrons (e−) of zinc manganate and carbon nitride are transferred to the conduction band (CB), while an equal amount of photogenerated holes (h+) are retained on the VB. Along the path of the Z-type heterostructure, it can be found that the electrons at the CB position in C3N4 migrate to the VB position of ZnMn2O4 and recombine with the photogenerated holes of ZnMn2O4. Since the CB position of ZnMn2O4 is more negative than O2/O2− (−0.33 eV vs. NHE), the electrons on the CB of ZnMn2O4 can effectively reduce O2 to O2−. The VB position of C3N4 is more correct than that of ZnMn2O4, which retains the strong oxidation of valence band holes of C3N4. Subsequently, the generated superoxide radicals, photogenerated holes, and hydroxyl radicals attack the SMX molecules, resulting in their degradation. Therefore, 50 wt% ZMOCN photocatalyst exhibits good photocatalytic activity.

4. Experimental Section

4.1. Materials

Anhydrous zinc acetate (C4H6O4Zn), manganese acetate dihydrate ((CH3COO)2Mn·2H2O), urea (CH4N2O), anhydrous ethanol (C2H5OH), and cyanamide (CH2N2) were purchased from Aladdin Reagents, China.

4.2. Synthesis

4.2.1. Synthesis of Zinc Manganate (ZnMn2O4) Nanosheets

The precursor of zinc manganate nanosheets was prepared using a hydrothermal method using zinc acetate and manganese acetate as raw materials and urea as pore-forming agent. The precursor was calcined to obtain zinc manganate nanosheets. The specific process was as follows: Weigh 0.01 mol zinc acetate and 0.02 mol manganese acetate, and completely dissolve them with a mixed solution of 15 mL deionized water and 15 mL absolute ethanol. Then 0.01 mol urea was added to 15 mL deionized water and dissolved. Pour the urea aqueous solution into the constant pressure drop funnel, control the drop acceleration, and stir while dropping to make it fully react. The reaction solution was transferred to a high-pressure reactor at 200 °C, and the reaction was continued for 20 h. After the reaction, the obtained brown suspension was centrifuged at 5000 r/min (2600 × g) for 10 min to obtain a brown solid. The solid was repeatedly washed three times with deionized water and ethanol solution to remove the incomplete reaction material. The obtained solids were placed in a vacuum drying oven (60 °C), dried for 12 h, and ground to a fine powder. The grounded powder was placed in a muffle furnace and calcined at 650 °C in air for 5 h to obtain dark brown ZnMn2O4 nanosheets.

4.2.2. Synthesis of Nitrogen-Deficient and Oxygen-Doped C3N4

A certain amount of cotton was immersed in 15 g cyanamide solution to wet the material completely. It was stirred continuously at room temperature for 1 h to mix the materials evenly, and the sample was then freeze-dried to remove the solvent. Finally, the dried sample was heated at 550 °C for 2 h in an air atmosphere to decompose the sample to obtain the required sample.

4.2.3. Synthesis of Three-Dimensional Nitrogen-Deficient ZnMn2O4/Carbon Nitride (ZMOCNs) Nanocomposites

Three-dimensional ZnMn2O4/carbon nitride (ZMOCNs) composites with different ZnMn2O4 contents were prepared using the calcination method. The mass fractions of ZnMn2O4 in the composites were 10 wt%, 30 wt%, 50 wt%, 70 wt%, and 90 wt%, respectively. Therefore, the preparation process described below is only reflected in individual cases. The amount of the actual experimental process is added in the mass fraction of 10 wt%, 30 wt%, 50 wt%, 70 wt%, and 90 wt% to obtain 10 wt% ZMOCN, 30 wt% ZMOCN, 50 wt% ZMOCN, 70 wt% ZMOCN, and 90 wt% ZMOCN composites. The preparation process is as follows: First, a certain amount of ZnMn2O4 powder was weighed and added to an appropriate amount of cyanamide solution. The ZnMn2O4 was completely dispersed in the cyanamide solution using ultrasonic oscillation. Then the same amount of cotton as a three-dimensional material template was put into the solution, continued to ultrasound until the solution was fully absorbed, and the material was freeze-dried for 24 h to remove excess solvent. Finally, the dried material was placed in a tube furnace and calcined at 550 °C for 2 h in a nitrogen atmosphere to obtain a three-dimensional ZnMn2O4/carbon nitride (ZMOCNs) composite. Figure 10 shows the preparation route of ZMOCNs composites.

5. Conclusions

In summary, we successfully prepared a three-dimensional multi-defect ZMOCN-50 wt% composite photocatalyst by growing C, O-doped and nitrogen-deficient C3N4 on the surface of zinc manganate nanosheets with different mass fractions. ZMOCN-50 wt% exhibits excellent light absorption and high catalytic activity. The results show that ZMOCN-50 wt% photocatalyst can remove 94.3% of SMX in 60 min without auxiliary catalyst and can achieve an ideal SMX removal efficiency in different water environments. The ZMOCN-50 wt% composite photocatalyst still has high stability after the fourth photocatalytic cycles. In addition, the three-dimensional structure of ZMOCN-50 wt% avoids the awkward problem of catalyst recovery. Therefore, the ZMOCN-50 wt% prepared in this study can be used as a promising photocatalyst in the field of environmental remediation.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal13010172/s1, Figure S1: The XRD patterns of original C3N4 and multi-defect C3N4; Figure S2: The XRD patterns of ZnMn2O4 and ZMOCN-90 wt%; Figure S3: UV–Vis DRS of original C3N4 and multi-defect C3N4; Figure S4: The corresponding (𝛼h𝜈)2 versus h𝜈 curves of original C3N4 and multi-defect C3N4; Figure S5: Mott-Schottky plots of C3N4 (a) and ZnMn2O4 (b), respectively; Figure S6: SEM images of C, O doped C3N4 with nitrogen defects; Figure S7: (a) TEM images of C, O doped C3N4 with nitrogen defects. (b–d) Mapping diagram of C, O doped C3N4 with nitrogen defects; Figure S8: SEM images of ZnMn2O4 nanosheets; Figure S9: The TEM image of ZnMn2O4; Figure S10: The MS spectra of degraded SMX; Table S1: The ICP results of ZMOCNs particles; Table S2: The peak area.

Author Contributions

Conceptualization, methodology, and investigation, Y.X. and Y.L.; writing—original draft preparation, Y.X. and L.Z.; methodology, resources, funding acquisition, writing—review and editing, J.L.; writing—review and editing, C.G. All authors have read and agreed to the published version of the manuscript.

Funding

This work is supported by the Hainan Provincial Key Research and Development Program (ZDYF2020222), Hainan Province Science and Technology Special Fund (ZDYF2022SHFZ094), and National Natural Science Foundation of China (22166016).

Data Availability Statement

The data presented in this study are available in [insert article or Supplementary Material here].

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) XRD patterns of ZnMn2O4, C3N4, ZMOCN-10 wt%, ZMOCN-30 wt%, ZMOCN-50 wt%, ZMOCN-70 wt% and ZMOCN-90 wt%, respectively. (b) Infrared Spectroscopy (IR) of ZnMn2O4, C3N4, ZMOCN-10 wt%, ZMOCN-30 wt%, ZMOCN-50 wt%, ZMOCN-70 wt% and ZMOCN-90 wt%, respectively.
Figure 1. (a) XRD patterns of ZnMn2O4, C3N4, ZMOCN-10 wt%, ZMOCN-30 wt%, ZMOCN-50 wt%, ZMOCN-70 wt% and ZMOCN-90 wt%, respectively. (b) Infrared Spectroscopy (IR) of ZnMn2O4, C3N4, ZMOCN-10 wt%, ZMOCN-30 wt%, ZMOCN-50 wt%, ZMOCN-70 wt% and ZMOCN-90 wt%, respectively.
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Figure 2. (a) XPS spectra of ZMOCN-50 wt%, high-resolution XPS spectrums of (b) C 1s, (c) N 1s, (d) O 1s, (e) Zn 2p, and (f) Mn 2p of ZMOCN-50 wt%, respectively.
Figure 2. (a) XPS spectra of ZMOCN-50 wt%, high-resolution XPS spectrums of (b) C 1s, (c) N 1s, (d) O 1s, (e) Zn 2p, and (f) Mn 2p of ZMOCN-50 wt%, respectively.
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Figure 3. EPR spectra (a) of C3N4 and ZMOCN-50 wt%. (b) UV–Vis DRS of ZMOCNs. (c) The corresponding (𝛼h𝜈)2 versus h𝜈 curves of ZMOCNs.
Figure 3. EPR spectra (a) of C3N4 and ZMOCN-50 wt%. (b) UV–Vis DRS of ZMOCNs. (c) The corresponding (𝛼h𝜈)2 versus h𝜈 curves of ZMOCNs.
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Figure 4. SEM image of (a) 10 wt% ZMOCN, (b) 30 wt% ZMOCN, (c) 50 wt% ZMOCN, (d) 70 wt% ZMOCN (e) 90 wt% ZMOCN, and (f) TEM image of 50 wt% ZMOCN.
Figure 4. SEM image of (a) 10 wt% ZMOCN, (b) 30 wt% ZMOCN, (c) 50 wt% ZMOCN, (d) 70 wt% ZMOCN (e) 90 wt% ZMOCN, and (f) TEM image of 50 wt% ZMOCN.
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Figure 5. (a) photocatalytic degradation of SMX under simulated sunlight irradiation. (b) Photocatalytic degradation of SMX in different waters under simulated sunlight irradiation. (c) Degradation rate and stability. (d) Photocatalytic degradation efficiency of SMX over the ZMOCN-50 wt% with different quenchers.
Figure 5. (a) photocatalytic degradation of SMX under simulated sunlight irradiation. (b) Photocatalytic degradation of SMX in different waters under simulated sunlight irradiation. (c) Degradation rate and stability. (d) Photocatalytic degradation efficiency of SMX over the ZMOCN-50 wt% with different quenchers.
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Figure 6. EPR spectra under dark and visible-light irradiation: (a) DMPO-O2- of ZMOCN-50 wt% and (b) DMPO-OH of ZMOCN-50 wt%.
Figure 6. EPR spectra under dark and visible-light irradiation: (a) DMPO-O2- of ZMOCN-50 wt% and (b) DMPO-OH of ZMOCN-50 wt%.
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Figure 7. Possible pathways of SMX degradation.
Figure 7. Possible pathways of SMX degradation.
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Figure 8. Predicted acute and chronic toxicity of SMX and its degradation intermediates using ECOSAR system.
Figure 8. Predicted acute and chronic toxicity of SMX and its degradation intermediates using ECOSAR system.
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Figure 9. The schematic diagram of photocatalytic pollutant degradation by ZMOCN-50 wt%.
Figure 9. The schematic diagram of photocatalytic pollutant degradation by ZMOCN-50 wt%.
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Figure 10. Schematic illustration of the synthesis of nitrogen-deficient ZMOCNs.
Figure 10. Schematic illustration of the synthesis of nitrogen-deficient ZMOCNs.
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Xu, Y.; Liao, J.; Zhang, L.; Li, Y.; Ge, C. Construction of Multi-Defective ZnMn2O4/Carbon Nitride Three-Dimensional System for Highly Efficient Photocatalytic Sulfamethoxazole Degradation. Catalysts 2023, 13, 172. https://doi.org/10.3390/catal13010172

AMA Style

Xu Y, Liao J, Zhang L, Li Y, Ge C. Construction of Multi-Defective ZnMn2O4/Carbon Nitride Three-Dimensional System for Highly Efficient Photocatalytic Sulfamethoxazole Degradation. Catalysts. 2023; 13(1):172. https://doi.org/10.3390/catal13010172

Chicago/Turabian Style

Xu, Yandong, Jianjun Liao, Linlin Zhang, Yakun Li, and Chengjun Ge. 2023. "Construction of Multi-Defective ZnMn2O4/Carbon Nitride Three-Dimensional System for Highly Efficient Photocatalytic Sulfamethoxazole Degradation" Catalysts 13, no. 1: 172. https://doi.org/10.3390/catal13010172

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